1. Field of the Invention
This invention relates to a copper based alloy having excellent blankability as well as good corrosion resistance and high strength, which is suitable for use as materials for electrical and electronic parts, such as lead frames, terminals, connectors, and caps for crystal oscillators, keys, springs, buttons, tableware, ornaments, and golf clubs. Especially, a copper based alloy according to the invention exhibits excellent effects when used as a material for keys.
2. Prior Art
Conventionally, brass having a typical composition of Cu-40% by weight Zn is widely used as a material for keys (hereinafter referred to as "the key material"). However, brass is poor in strength and corrosion resistance, resulting in that keys formed of brass are likely to corrode, and further, they can be deformed when they are made thinner to be lighter in weight. To overcome these disadvantages, there has been proposed a key material formed of a high-strength copper based alloy (hereinafter referred to as "the Cu alloy") which is excellent in corrosion resistance, for example, by Japanese Laid-Open Patent Publication (Kokai) No. 5-171320. The Cu alloy has a chemical composition consisting essentially, by weight percent (hereinafter referred to as "%"), of 15 to 35% Zn, 7 to 14% Ni, 0.1 to 2% exclusive Mn, 0.01 to 0.5% Fe, 0.001 to 0.1% p, and the balance of Cu and inevitable impurities.
Although the above proposed high-strength Cu alloy is excellent in corrosion resistance, it is poor in blankability. As a result, keys manufactured by blanking or stamping the high-strength Cu alloy key material has a blankout section which does not have satisfactorily close dimensional tolerances.
Generally, a blankout section 3 of a key obtained by blanking a Cu alloy key material in the direction indicated by an arrow A in the single figure consists of a shear section 2 and a rupture section 1, and in evaluation of the key material, it is regarded that the larger a ratio of the rupture section 1 to the entire blankout section 3 (hereinafter referred to as "rupture section ratio"), the more excellent in blankability the key material. A blankout sheet material is generally required to have a rupture section ratio of 75% or more.
When the above proposed high-strength Cu alloy key material is subjected to blanking to obtain keys, however, the blankout section 3 of the resulting keys has a rupture section ratio less than the required value of 75%. As a result, blanking dies used to blank the high-strength Cu alloy key material become shorter in service life, and further the blankout section of the keys does not have satisfactorily close dimensional tolerances, which unfavorably leads to a shortened service life of the dies as well as an increased amount of after-treatment, and hence an increased manufacturing cost.